Low-permeability reservoir stratums are generally developed with microcracks, and the microcracks can be communicated with a relatively large seepage channel in the substrate hole and reservoir stratum, and improve the permeability of the substrate. It plays an important role improving the flow condition of fluid in stratum and increasing the production of an oil well. Physical simulation is an important means of stimulating the development of oil and gas reservoir. Practice shows that the larger the physical dimension of the model is, the more practical the experimental result to the oil field is. Experimental cores include a natural core and a man-made core, and since it is difficult to obtain the core with a microcrack that is easy to be broken, the man-made core is generally used in the experiment. Since the size of a drilling well to take the core is limited, the man-made core is more required to the large model. While the main focus is on the manufacturing of macrocracks, there is little research done in the manufacturing of microcracks, which a man-made method is usually used. For example, Chinese Invention Patent (201410260860.9) discloses a manufacturing method of a man-made core of a jointing shale, and provides that edible oatmeal with diameter of 5 to 8 mm is used in the cement sample to stimulate the microcrack, and the pattern of the stimulated microcrack is relatively simplex; Chinese Invention Patent (201510004960.X) discloses a manufacturing method of a hard brittle shale microcrack and a test system of sealing capacity, a shale crack maker is used to make the core crack, the dedusting and sculpture are conducted to the crack surface, half of it is stacked with a sluggish strip material with width of 2 mm and different thickness along edges of two longitudinal side, which stimulates the microcrack with different width ranging from 10 to 100 um, but the core used is standard core column with diameter of 25 mm and length of 30 mm.
Some scholars put forward that a uniform splitting method can stimulate the natural microcrack (Jia Hu, et al., Research on Physical Simulation Experiment Method of Fracture-cave Oil and Gas Reservoir, Vol. 38 No. 6, 2010), but this method needs to cut the core into two equal parts, the crack surface is relatively straight and smooth, and does not comply with the actual pattern of the microcrack, and it is difficult to manufacture multiple microcracks.
In 2014, Gao Tianfang from Chinese Academy of Sciences put forward in his master's thesis “Research on Ultra-low Permeability Reservoir Plane Physical Simulation Method” that the crack was cut by a sand wire, the width of the crack was controlled through adjusting the thickness of the sand wire, but there was a condition that the pattern of the crack surface did not comply with the actual pattern.
In 2014, Teng Qi from Chinese Academy of Sciences manufactured the microcrack by a method of conducting triaxial compression to one-dimensional core in his doctoral thesis “Crack Ultra-low Permeability Reservoir Physical Simulation Experiment Method and Application”. This method was possible to form multiple cracks, but this method used many devices in generating cracks. The pressure used in generating crack was large, and the operation method was relatively complicated.
The stone can generate microcrack by a heating method, and the method is a traditional heating method and a microwave heating method. The heating is uneven by the traditional heating method and the transmission of the heat energy is relatively slow, and the microwave heating method can generate the problem of radiation security if it is improperly used.